Everyone is different — I tend to enjoy sex that lasts an hour or two at a time, multiple times in a row. But a lot of women aren’t into that, so one adjusts based on one’s partner. And as for a technique that stops you from cumming, I can’t imagine wanting to learn such a thing. For me, duration is a function of enjoyment. The more I’m enjoying it, the less I want to reach the conclusion. This is what makes it organic rather than being a performance. So I can’t advise any man to embrace Uncle Google in the hope of finding some technique (counting backward? imagining Trump naked?) that will stave off ejaculation; far better to go with the flow and really truly be present. After that, everything follows naturally.
As for telling your boyfriend/husband/partner, that’s a very personal and individual thing. For myself I love to listen and learn, but I have at my advanced age no illusions and no insecurities. For others, especially for younger men in the USA, it is likely very different.